The present exemplary embodiment relates generally to electrophotographic printing. It finds particular application in conjunction with setting the target of a toner concentration sensor in an electrophotographic printing machine, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In xerographic print engines, there is normally a toner concentration (TC) sensor located in the sump of the developer housing. Most low cost TC sensors only output only relative TC information, not absolute TC information. Also TC variability from the same sensor target is due to several factors, including sensor manufacturing variability, environmental changes, developer aging characteristics, and characteristics of sensor aging due to mechanical wear. In the past, to determine if the TC level is correct, xerographic systems used expensive calibrated LED bars called patch generators to produce continuous tone control patches to set up the TC. For these reasons, a method is required to set up the target for the sensor, so that TC in the development housing meets the xerographic system requirements.
Such a method, however, requires the use of a development curve model. In Xerographic marking engines, the relationship between solid developed mass and development voltage, also called a development curve, plays an important role in xerographic process controls, diagnostics, and system integration. It is not realistic and nearly impossible to generate a development curve in the field. It is very time consuming and needs special equipment to remove toner from the photoreceptor in a controlled fashion and measure it. In practical applications, a development curve can be obtained by using a transmission densitometer to get referred DMA (developed mass per unit area). Compared to a reflection densitometer, a transmission densitometer is much more expensive and its reliability is not as good. Also, a development curve is a nonlinear function, which presents a challenge to develop a robust algorithm to estimate the parameters of the development curve model in real time.
Thus, there is a need for a new method by which the target of a toner concentration (TC) sensor can be set up based on the equivalent developability concept without using an expensive patch generator. There is also a need for a new strategy and method to generate a model of the development curve in real time using a low cost reflection densitometer. Instead of modeling the development curve directly, a pseudo development curve model is needed, based on the relationship of toner area coverage (TAC) and the development voltage Vdev due to the saturation of the reflection sensor at high DMA. This pseudo development curve model is very similar to the real development curve and is sufficient for most applications in xerographic process controls, diagnostics, and integration.